threading_timer_decorator_exit.py

####### License: MIT
"""MIT License

Copyright (c) 2020 Mavaddat Javid and Aaron Hall

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
"""
from __future__ import print_function # ignore for Python 3

import sys
import threading
from time import sleep
try:
    import thread
except ImportError:
    import _thread as thread
    
try: # use code that works the same in Python 2 and 3
    # ignore this for Python 3
    range, _print = xrange, print
    def print(*args, **kwargs): 
        flush = kwargs.pop('flush', False)
        _print(*args, **kwargs)
        if flush:
            kwargs.get('file', sys.stdout).flush()            
except NameError:
    pass



def cdquit(fn_name):
    # print to stderr, unbuffered in Python 2.
    print('{0} took too long'.format(fn_name), file=sys.stderr) # print the "`fn_name` took too long" to error output stream
    sys.stderr.flush() # Python 3 stderr is likely buffered.
    thread.interrupt_main() # raises KeyboardInterrupt
    
def exit_after(s):
    '''
    :param: s integer
    use this function as decorator for function `fn` to exit process if 
    function `fn` takes longer than `s` seconds for arguments `args` and `kwargs`
    '''
    def outer(fn):
        def inner(*args, **kwargs): # *args is a `list` object of arguments, **kwargs is a `dictionary` object of key-walkable arguments 
            # `s` is number of seconds as param for `exit_after`
            # 'fn' is the callback function as param for `outer`
            timer = threading.Timer(s, cdquit, args=[fn.__name__])
            # create a threading timer with `s` seconds after which timer quits using `cdquit` function and send timer `args` with one element, which is the name of the callback function `fn`
            timer.start() # start the timer
            try:
                result = fn(*args, **kwargs) # try to call the callback with params `args` and `kwargs`
            finally:
                timer.cancel() # whether fail or success, afterward cancel the timer (if function ended before timer completes)
            return result # return the `result` of callback `fn` with params `args` and `kwargs`
        return inner # return result of `inner` function, which is `result` of callback function `fn`
    return outer # return result of `outer` function, which is `result` of callback function `fn` passed along from `inner`
    
@exit_after(1)
def a():
    print('a')

@exit_after(2)
def b():
    print('b')
    sleep(1)

@exit_after(3)
def c():
    print('c')
    sleep(2)

@exit_after(4)
def d():
    print('d started')
    for i in range(10):
        sleep(1)
        print(i)

@exit_after(5)
def countdown(n):
    print('countdown started', flush=True)
    for i in range(n, -1, -1):
        print(i, end=', ', flush=True)
        sleep(1)
    print('countdown finished')

def main():
    a()
    b()
    c()
    try:
        d()
    except KeyboardInterrupt as error:
        print('d should not have finished, printing error as expected:')
        print(error)
    countdown(3)
    countdown(10)
    print('This should not print!!!')
    

if __name__ == '__main__':
    main()